Such a method is used, for example, in GSM mobile-radio systems (GSM=Global System for Mobile Communications).
There, each mobile station has a mobile equipment identity number allocated to it, the IMEI. This equipment number can be requested by the respective mobile switching center (MSC).
The mobile switching centers, in turn, have an equipment identity register (EIR), which contains data about, e.g., mobile stations that have been reported stolen.
Before establishing a connection for a mobile-radio subscriber, the mobile switching center requests the equipment number of the subscriber's mobile station. Then it checks by means of the equipment identity register whether the mobile station has been reported stolen or not. If it has been stolen, the mobile switching center will refuse to set up the call.
In a book by M. Mouly and M. B. Pautet, "The GSM System for Mobile Communications", ISBN Number 2-9507190-0-7, the structure of such an equipment identity register is explained in the chapter entitled "Mobile Equipment Management".
Three lists, referred to as "white list", "grey list", and "black list", are stored in the equipment identity register.
The white list contains ranges of equipment numbers of mobile stations which operate properly and have not been stolen. The black list contains equipment numbers for mobile stations which have been stolen or do not operate properly. The grey list contains equipment numbers for mobile stations whose status has not been finally determined, i.e., for example, before black-listing is imposed.
How these lists are stored in the equipment identity register and how they are searched for a given equipment number is not described.
In general, there are two possibilities:
One is to search the equipment lists successively for a given equipment number.
The other is to create a common list which contains all equipment numbers along with the respective equipment list to which they are assigned. Such a list may be sorted according to a particular criterion, whereby the search for a given equipment number is speeded up.
Since each mobile station is provided with an equipment number, the total of equipment numbers is very large. This results in large data sets for each of the above-described possibilities, which require much storage space and in which the search for an equipment number takes relatively long.